About Me

Thursday, June 30, 2011

Ans. Moen-Jo-Daro means “Mound of the Dead”. It is situated at a distance of 27km from Larkana on the right bank of river Indus.

Q.2 Who was Sir John Marshall?

Ans. Sir John Marshall was an English civil servant, whose work was to look after historical remains, like ancient building and other old things such as these pieces of pots and bricks. He was very interested in history and was anxious to find out about these remains.

Q.3 What did Sir John Marshall remark, when pieces of old pots and bricks were brought to him?

Ans. sir John Marshall was an English civil servant who was interested in old historical remains. So when some villagers brought pieces of old pots and bricks he at once know that they were pieces of historical remains.He remarked that perhaps these was an ancient city lying under the mound of day and sand. He directed the villagers to dig there in the hope that they would uncover the remains of an ancient city.

Q.4 What was the occupations of the people of Moen-Jo-Daro?

Ans. The people of Moen-Jo-Daro were traders. They traded with other cities and traveled from place to place on business.They were skilled craft men who worked with gold and silver.They were farmers who grew wheat, rice and cotton and they also kept cattle.

Q.5 How was the city of Moen-Jo-Daro planned?

Ans. The city of Moen-Jo-Daro was a well planned and cleaned city. Each house was made of large baked bricks and a bathroom and servant-quarters close by covered drains beside the streets. The streets were made of baked bricks.There was a great hall where grain were stored. There is a wide road in the middle of which was the shopping centre with shops on both sides.

Q.6 Name any four objects on exhibition in the Moen-Jo-Daro Museum? or Name any four findings of Moen-Jo-Daro?

Ans. The objects found in Moen-Jo-Daro are:1. A metal statue of a dancing girl.2. Seals, Gold, Silver and Ivory Jewelery.3. Painted Pottery4. Metal tools and weapons.5. The head of a bull.

Q.7 How old is the civilization of Moen-Jo-Daro?

Ans. The civilization of Moen-Jo-Daro is 4500 years old.

Q.8 How did this civilization come to an end?

Ans. No body knows exactly how this ancient civilization came to an end. Either they were from the north or some great earthquake destroyed them.

Q.9 How do we know Moen-Jo-Daro’s probable age? What can help us to know more about civilization?

Ans. We know Moen-Jo-Daro’s probable ge from the metal objects found from the execution. We can learn more about this civilization if the language experts are able to determine the meanings of the words written on the seals and the pottery.

Q.1 How can the Neem Tree prevent the burning heat of the sun from troubling us?

Ans. The high Neem Tree with its extending branches interrupts the scorching heat of the mid day sun and provide soothing shade to people. In this way, it prevents the burning heat of the sun from troubling us.

Q.2 Why does the poetess say that Neem Tree is unafraid?

Ans. The poetess Mrs. Elsa Kazi says that the Neem Tree is unafraid of the burning heat of the sun and stands unprotected and unrefreshed the whole day long in the scorching heat of the sun.

Q.3 What does the Neem Tree look like?

Ans. The Neem Tree looks like a man, facing every fate in life, boldly and bravely.

Q.4 How does the poetess compare the Neem Tree to man?

Ans. The Neem tree provides shelter to people and protects them from the scorching heat of the sun without any protection for itself. It stands out in the open hot sun bearing the fierce heat. In the someway, man can be as fold as the Neem tree and try to protect his fellow human beings from sorrow and poverty by sacrificing his own comfort.

Q.5 What according to the poetess is the highest aim in life?

Ans. A man must hold with determination for all kinds of difficulties in life and accept the ups and downs of life in a stead fast manner. Through self sacrifice he must help his fellow human beings who are poor, sad and in trouble and guide them on the right path. This, according to Mrs. Elsa Kazi is the highest aim of the life.

Ans. Shah Abdul Latif was a great saint who is lovingly called “Lal Latif” by his devotees. He was born in a small village called “Hala Haveli” in the year 1689.

Q.2 What do you know about the ancestors of Shah Abdul Latif?

Ans. Shah Abdul Latif’s ancestors had migrated to Sindh during the days of Tamerlane. They had come from Hiirat a town in West Afghanistan. They liked Sindh so much so that they decided to make it their permanent home. Many centuries later one of their decendants, Syed Habib Shah, was blessed with a son who grew up to be “Saint Lal Latif”.

Q.3 Why is Shah Latif known as “Saint of Bhit”?

Ans. When Shah Latif father died, he left his home and went to live on a Mound at some distance from his village. A mound of sand is called “Bhit” in Sindhi. Due to the fact that he lived on this mound for the rest of his life, Shah Latif came to be known as “The Saint of Bhit.”

Q.4 Name the shrines of saints found in Pakistan.

Ans. In every part of our country, there are shrines of such saints:In Lahore, The shrines of Data Ganj Bakhsh and Mian Mir Sahib.In Pak Pattan, Lived and Died Baba Fareed.In Multan, The Shrine of Ghoues Bahaul Haq.In Sindh, the Shrines of Shah Abdul Latif and Qalander Lal Shahbaz.In Peshawar, in Quetta, and in countless other towns and cities there are the tombs of these man of God.

Q.5 What are the important features of Shah Latif poetry?

Ans. The important features of Shah Latif’s poetry is that it is written in the language of the common people, and other great quality of his poetry beside its simplicity is its moving music.

Q.6 What is the message of Shah Latif’s poetry? or What according Shah Latif is the goal of life?

Ans. The message of Shah Latif is the message of love. He believed in the brotherhood and equality of men and in pleasing God by good deeds. This according to Shah Latif is the goal of life.

Q.7 When is the Urs of Shah Abdul Latif’s held?

Ans. Shah Abdul Latif Urs is held at his shrine every year on 14th Safar, the second, month of the muslim calender.

Q.8 How do Shah Latif’s devotees celebrate his Urs?

Ans. Shah Latif’s Urs is held at his shrine every year in 14th Safar, the second month of the Muslim calender. Thousands of people gather to listen to the Saint’s song sung to the Tambooro and after their prayers. Many learned men read papers that tell about Latif’s life and poetry.

Q.9 What do you know about Shah Latif’s music?

Ans. Shah Latif was not only a saint and a poet but also a great musician. He found great comfort in music. His skill in this art enabled him to make many improvements and changes in the difficult music of his time. He loved simplicity in music and musical instruments. He did not agree with the idea that music should be difficult. So he made it simple and also vented on instrument called “Tambooro”.

Q.10 What do you know about Tamboora?

Ans. The tambooro is a simple musical instrument invented by the Sufi, philosopher Shah Abdul Latif.

Q.11 Write a short note on the poetry of Shah Abdul Latif?

Ans. Shah Abdul Latif started composing poetry while he was only a boy. Shah Abdul Latif was a mystic poet. He was a versatile, genious and had attempted all aspects of poetry.Shah Abdul Latif was a poet of the people and was successful in awakening them to the discovery of the truth of spiritual life. He had very deed sympathy for the poor and had expressed in his sentiments about them with great pathos and fubings.His collection of poems was so valued that it was translated into many languages and is called “Risalo of Shah Latif.”

Ans. Hazrat Mohammad (P.B.U.H) the prophet of Islam was born in the year 571 A.D at Makkah.

Q.2 To which tribe did Prophet Mohammad belong? What did they believe in?

Ans. Prophet Mohammad belonged to the noble family of Quraish. They believed and worshiped idols and did not believe in one God.

Q.3 What did Prophet Mohammad (P.B.U.H) ask the Quraish to do?

Ans. Hazrat Mohammad (P.B.U.H) asked the Quraish not to worship their false Gods and asked them to worship the one and the only true God.

Q.4 Why did Prophet Mohammad (P.B.U.H) migrate to Madina?

Ans. Most of the people of Makkah refused to accept Islam. They opposed the new faith and their bitter opposition cause the Prophet (P.B.U.H) much agony and a lot of trouble. So in 622 A.D. Prophet Mohammad (P.B.U.H) migrated to Madina.

Q.5 What is Hijra? Where did it take place?

Ans. In 622 A.D the prophet Mohammad (P.B.U.H) accompanied by his faithfully friend Hazrat Abu Bakr migrated to Madina. This count is known in history as the “Hijra”.

Q.6 On what principles was the Islamic Society founded?

Ans. In Madina the Prophet (P.B.U.H) founded the Islamic Society based on the three principles:

* All power belongs to Allah. * Mohammad (P.B.U.H) is his Prophet. * All Muslims are brothers to one another.

Q.7 What does the last sermon teach us?

Ans. In the 10th year of Hijra the Prophet (P.B.U.H) together with his followers went to perform Hajj at Makkah. There he addressed a very large gathering of muslims at mount Aarafat. This was the last sermon of the Holy Prophet (P.B.U.H).It teaches us that there is no God Except Allah. Only the goodness of a person makes him superior to others. The most righteous is the most honourable. All Muslims are brother to one another. Finnally the last sermon teaches us that the Holy Quran is the message of Allah and if we act according to its teachings, we will never go wrong.

Q.8 Why did the Quraish oppose the Holy Prophet (P.B.U.H)?

Ans. The Holy Prophet asked the Quraish not to worship there false Gods but to worship the One and only true God and to accept him as the Prophet of God. However, they refuse to do so and believe that he was preaching against their Gods, and their ancestors. So they oppose the new religion of Islam and their fierce and terrible oppositions made it impossible for the Prophet (P.B.U.H) to continue being in Makkah and compelled him to leave that city, Makkah.

The acidity of a base is defined as the number of ionizable hydroxyl groups in its molecule.

Anode

It is an electrode through which electrons enter the external circuit.

Alpha Rays

There are positively charged particles emitted from a radioactive substance. They carry two positive charges and are called helium nuclie.

Analytical Chemistry

It is the branch of chemistry which discusses the analytical methods forgetting information about chemical compounds and chemical processes.

Atomic Number

Number of positively charged particles (protons) present in the nucleus of an atom.

Atomic Size

Average distance between the nucleus of an atom and its outermost electronic shell. Its units are nm or pm.

Arrehenius Acid

It is a chemical compound which gives proton (H+) in water.

Arrehenius Base

It is a chemical compound which gives hydroxide ion (OH-) in water.

Atomic Spectrum

Spectrum of radiations emitted by the excited atoms when they come to the normal state.

Acidic Salts

An acidic salt is obtained when hydrogen atoms present in an acid, are partially replaced by metallic atoms.

Alchemist

A scientist trying to convert cheaper metals into precious metals is called Alchemist and this branch of chemistry is called Alchemy.

Atomic Mass

The mass of an element relative to the unit mass, which is 1/12th o the mass of C-12.

Ampere

The amount of electric current which liberate one electrochemical equivalent of a substance per second during electrolysis of that substance is called ampere.

Biochemistry

It is the study of chemical compounds present in living things.

Balancing of Chemical Equations

Equating the atoms of reactants with those of products.

Beta Rays

These are electrons emitted from a radioactive substance.

Brownian Movement

The free movement of the molecules of gases and liquids is called Brownian movement.

Bronsted Acid

A compound which can donate proton.

Bronsted Base

A compound which can accept proton.

Basicity

The basicity of an acid is defined as the number, of ionizable hydrogen atoms present in its molecule.

Basic Salts

A basic salt is obtained when the hydroxyl groups present in a base are partially replaced by some other groups.

Boiling Point

A temperature at which a liquid changes into gaseous state.

Chemistry

The branch of science, which deals with the composition of matter changes in matter and the laws or principles which govern these changes.

Chemical Equation

The representation of a chemical change in terms of symbols and formulas.

Covalent Solid

A solid in which there exist a covalent bond between atoms.

Covalent Bond

It is the force of attraction that arises between two atoms due to mutual sharing of an electron pair.

Co-Ordinate Covalent Bond

When the shared pair of electrons is provided by one of the bonded atoms, a coordinate covalent bond is formed.

Cohesive Forces

The forces of attraction present between the particles of solid, liquid and a gas.

Cathode Rays

Rays emitted from cathode in the discharge tube.

Colloidal Solution

A solution in which solute particles are bigger than those present in a true solution and which cannot be filtered.

Conductor

A substance which allows electric current to pass through it.

Cathode

It is an electrode through which electrons leave the external circuit.

Concentration of a Solution

The amount of a solute which has been dissolved in a particular amount of a solvent.

Concentrated Solution

A solution, which contains an excess amount of a solute as compared to that of a solvent.

Cell

The vessel containing reacting substances in which transfer of electrons takes place is called cell.

Coulomb

It is unit of electric current. When one ampere electric current is passed for one second the quantity of electric current is one coulomb.

Discharge Tube

A glass tube containing a gas at a very low pressure and provided with electrodes to study the passage of electricity through the gas.

Dipole-Dipole Forces

The forces of attraction which originate due to the difference in electro negativities of the bonded atoms in polar molecules.

Diffusion

The movement of molecules from a higher concentration to a Lowr concentration is called Diffusion.

Dilute Solution

A solution, which contains a small amount of a solute as compared to that of a solvent.

Double Salts

When two typical salts are crystallized together a double salt is formed. The physical properties of the crystals of double salt are different from those of the component salts.

Doberiner’s Law of Triads

Dobereiner arranged similar elements in sets of three, called Triads. Atomic mass of the middle atom of a triad was equal to the average of the atomic masses of first and third members.

Degree of Ionization

It is the extent to which an electrolyte ionizes in water.

Experiment

An experiment is an activity performed under suitable conditions with specially designed instruments to get the required information.

Empirical Formula

The formula of a compound which shows the minimum ratio present between the atoms.

Electron Affinity

The amount of energy given out when an electron is absorbed in the outermost electronic shell of all isolated gaseous atom. Its units are KJ/mol.

Electro-Negativity

It is the power of an atom to attract the shared pair of electrons.

Evaporation

The continuous escape of the molecules of a liquid from its surface.

Elastic Collision

When gas molecule collides with each other their total energy does not decrease or increase. This type of collision is called an elastic collision.

Electrolytic-Cell

In a non-spontaneous oxidation-reduction reaction takes place with the help of electrical energy.

Electro-Chemistry

It is that branch of chemistry in which chemical energy is converted into electrical energy or electrical energy is converted into chemical energy.

Electrolytes

When electricity is passed through an ionic compound which is either in the fused state or in the form of aqueous solution, it is decomposed into its constituents. The ionic compound is called an electrolyte.

Electrolysis

The passage of electricity through an electrolyte is called electrolysis.

Electrochemical Series

A list of ions in which they are arranged in the order of their ability to get discharged.

Electroplating

The process of depositing a metal on another metal with the help of electricity.

Exothermic Reaction

Those chemical reactions during which heat is evolved.

Endothermic Reactions

Those chemical reactions in which heat energy is absorbed.

Enthalpy of Reaction

Heat of reaction which takes place at constant pressure.

Formula Mass

Formula mass is the mass of compound relative to the unit mass which is 1/12th of the mass of C-12.

Farad

It is the unit of charge 1 farad = 96500 coulomb.

Fusion

When a solid change into liquid this phenomena is called Fusion.

Heat of Neutralization

The heat given out during a neutralization reaction is called heat of neutralization.

Heat of Reaction

Heat evolved or absorbed during a chemical reaction which takes place at pressure.

Hypothesis

In the light of experiments, the scientists try to explain observations and facts. This tentative explanation is called hypothesis. It is quite possible that after sometime, on the basis of new experiments this hypothesis may be rejected.

Hydrogen Bonding

When a hydrogen atom is attached to any one of fluorine, oxygen and nitrogen atoms, there appears strong dipole forces which are called hydrogen bonding.

Hydrated Ions

Ions of a solute surrounded by water molecules are called hydrated ions.

Ionization

An electrolyte splits up into charged particles upon heating or in its aqueous solution. This process is called Ionization.

Ionic Theory

A theory which explains the process of electrolysis.

Intermolecular Forces

The forces of attraction present between the molecules of a compound.

Ionization Energy

The minimum amount of energy required to remove an electron from the outermost electronic shell of an isolated gaseous atom. Its unit is KJ/mol.

Ionic Bond

A bond formed due to the electrostatic force of attraction between oppositely charged ions.

Ionic Solid

A solid which is made up of ions of opposite charges.

Isotope

Atoms of an element having the same atomic number but different mass number.

Inorganic Chemistry

The study of all elements and their compounds except carbon is called inorganic chemistry.

Industrial Chemistry

The application of chemical knowledge in technology and industry and the preparation of industrial products are called industrial chemistry.

Inference

To deduce results after coordinating the observed facts with integrated scientific knowledge is called inference.

Kinetic Theory

The theory which explains the composition and properties of all the three states of matter.

Lewis Acid

A substance which can accept an electron pair.

Law

A theory when repeatedly gives the same results after experimentation and offers correct explanation of scientific facts it then becomes a law or principle.

Law of Conservation of Mass

Total mass of reactants is equal to that of products during a chemical reaction.

Law of Definite

A compound always contains elements combined together in a fixed ratio by mass.

Law Multiple Proportions

When two elements combine together to give more then one compounds, the different masses of an element, which combine with the fixed mass of the other element, have a simple ratio between them.

Law of Reciprocal Proportions

When two or more elements A and B combine separately with the fixed mass of the third element E the ratio in which they do so may be the same or some simple multiple of the ratio in which these two elements (A and B) combine with each other.

Molar Solution

A solution in which one mole of a solute has been dissolved in one dm3 of solution. It is represented as M.

Metallic Bond

When positively charged metal ions are held together by freely moving electrons, the bond formed is called a metallic bond.

Molecular Solid

A solid which has Vander Waal’s forces present between its molecules.

Melting Point

A temperature at which a solid changes into a liquid.

Mass Number

The total number of protons and neutrons present in the nucleus of an atom.

Mendeleyv’s Periodic Law

Properties of elements are a periodic function of their atomic masses.

Modern Periodic Law

Properties of elements are a periodic function of their atomic numbers.

Molecular Mass

Molecular mass is the mass of an element or a compound relative to the unit mass, which is 1/12th of the mass of C-12.

Molar Mass

The mass of an element or a compound which contains Avogadro’s number particles.

Molecular Formula

The formula of an element or a compound which tells the actual number of atoms present in the molecule of that element or a compound.

Neutralization

Acids and bases react together to form salts and water and in this way they neutralize the properties of each other. This reaction is called Neutralization reaction.

Metals1. Metals have luster shine surface.2. Metals reflect heat and light.3. Metals conduct heat and electricity4. Metals are ductile and can be drawn into wire.

Non-Metals1. Non-Metals have no luster.2. Non-Metals usually don’t reflect heat and light.3. Non-Metals do not conduct heat and electricity.4. Non-Metals are non ductile and cannot be drawn into wire.5. Non-Metals are non-malleable and can not form sheets.

Homogeneous and Heterogeneous Mixture

Homogeneous Mixture1. Those mixtures, which have uniform composition throughout their mass are called homogeneous mixtures.2. Homogeneous mixture has only one phase through out its mass.3. Homogeneous mixture are also known as solution.4. Examples: Salt and water, Sugar and water.

Heterogeneous Mixture1. Those mixtures, which do not have uniform composition through their mass are called Heterogeneous Mixture.2. Heterogeneous Mixture has more than one phase through out its mass.3. Heterogeneous Mixture are not solutions.4. Examples: Rocks, Soil, Food products.

Molecular and Empirical Formula

Molecular Formula1. Formula which shows the actual number of atoms of each element present in a molecule is called Molecular Formula.2. Molecular Formula shows the structure of compound.3. Two or more compounds cannot have same Molecular Formula.4. Molecular Formula = n x Empirical Formula.5. It represents covalent compounds only.

Empirical Formula1. formula, which shows the relative ratio of atoms of each element present in a molecule, is called Empirical Formula.2. Empirical Formula can not show the structure of compound.3. Two or more compounds can have same Empirical Formula.4. Empirical Formula = Molecular Formula / n5. It represent an ionic compound as well as a covalent compound.

Symbol and Formula

Symbol1. A symbol is an abbreviation for the chemical name of an element and represents only one atom of the element.2. It represents one atom of an element.3. Symbol is written for elements.4. Examples: Na, Br, Cl, F etc.

Formula1. Representation of compound in terms of symbols is called formula. It represents one atom of an element.2. It represents atoms of same or different elements present in one molecule.3. It represents an ionic compounds as well as a covalent compound.4. Examples: H2O, NH3 etc.

Gram and Gram Molecule

GramThe atomic mass of an element expressed in grams is called gram atomic mass.2. It is associated with element only.3. It is the mass of one atomic mole.4. One gram atom of any substance contains 6.02 x 10(23) atoms. (23 is the power of 10).

Gram Molecule1. Molecular mass of any element or compound expressed in grams is called gram molecule.2. It is associated with element and compound.3. It is the mass of one molecular mole.4. One gram molecule of any substance contains 6.02 x 10(23) atoms. (23 is the power of 10).

Atom and Molecule

Atom1. It is the smallest particle of an element which can enter into a chemical reaction.2. It is represented by a symbol of the element.3. It shows the properties of the element.4. It retains its identity in a chemical reaction.

Molecule1. It is the smallest particle of a substance which can exist and show all the properties of the substance.2. It is represented by a molecular formula of the substance.3. It shows the properties of the substance.4. It does not retain its identity in a chemical reaction.

Exothermic and Endothermic Reactions

Exothermic Reaction1. Those chemical reactions in which heat energy is evolved are called exothermic reactions.2. In exothermic reactions the enthalpy of products is lower than the reactants. H is therefore negative for an exothermic reaction.3. During endothermic reaction, the system becomes colder and net potential energy of substance increases.4. The energy is absorbed during these reactions.5. The temperature of reaction therefore decreases.

Endothermic Reactions1. Those chemical reactions in which heat energy is absorbed are called endothermic reactions.2. In endothermic reactions the enthalpy of reactants is lower than the products. H is therefore positive in endothermic reaction.3. During endothermic reaction, the system becomes colder and net potential energy of substance increases.4. The energy is absorbed during these reactions.5. The temperature of reaction therefore decreases.

Physical and Chemical Properties

Physical Properties1. The physical properties of a substance are those characteristics which serve to distinguish it from other substance but do not deal with its ability to undergo chemical changes.2. These are related to the physical state of matter.3. Examples: Formation of ice from water, formation of a magnet from ice etc.

Chemical Properties1. The chemical properties of a substance indicate the ability of a substance to undergo chemical changes.2. They are related to the chemical change of a substance.3. Examples: burning of paper, rusting of iron.

Electrolyte and Non-Electrolyte

Electrolytes1. Electrolytes conduct electricity in molten or in solution form.2. These form positive and negative ions when dissolved in water e.g. NaCl form Na+ and Cl- ions when dissolved in water.3. Chemical changes occur when electric current is passed through the electrolyte.4. Generally these are ionic or polar covalent compounds.

Non-Electrolytes1. Non-electrolytes do not conduct electric current in molten or in solution form.2. These do not form positive and negative ions when dissolved in water e.g. Urea, sugar, glucose etc.2. No chemical change occurs in them on passing current.3. Generally these are non polar covalent compounds.4. Generally these are non polar covalent compounds.

Acid and Base

Acid1. Those compounds which provide hydrogen ion (H+) in aqueous solutions are called Acids.2. An acid is a substance which produces H+ ions in aqueous solution.3. Acid is a species (a compound or ion) which donates or tends to donate a proton (H+).4. An acid is a species (molecule or ion) which can accept a pair of electron. An acid is also called an electrophile (electron loving).5. They have sour taste.6. Acid turn blue litmus red methyl orange red.

Base1. Those compounds, which provides hydroxyl (OH-) ion in aqueous solution, are called bases.2. A base is a substance, which gives (OH-) in aqueous solution.3. A base is a species, which accepts or tends to accept a proton.4. A base is a species (molecule or ion) which can donate a pair of electrons. A base is also called a nucleophile (Nucleus loving).5. Bases have bitter taste.6. Bases turn red litmus to blue, colorless phenolphthalein to pink and methyl orange to yellow.

Ionic and Covalent Bond

Ionic Bond1. Ionic bond is formed by complete transfer of electrons from one atom to another atom.2. Ionic bond is always formed between different atoms. E.g. NaCl, CaCl2.3. In ionic bond atoms have very large electro-negativity and ionization energy difference.4. This bond is usually formed between metals and non-metals.5. This bond is very strong.6. As a result of this bond ionic compounds are formed.7. It is always formed between two different atoms.8. It is formed when difference of electro-negativity of combining atoms is 1.7 or more.

Covalent Bond1. Covalent bond is formed by the mutual sharing of electrons between two atoms.2. Covalent bond may be formed between similar or dissimilar atoms e.g. H2, O2, HCl etc.3. In covalent bond atoms have very small electro-negativity or ionization energy difference.4. This bond is usually formed between non-metals only.5. This bond is comparatively less strong.6. As a result of this bond covalent compounds are formed.7. It is formed between similar and different types of atoms.8. It is formed when difference of electro-negativity of combining atoms is less than 1.7.

Ionic and Covalent Compounds

Ionic Compounds1. The ionic compounds are usually solid, hard and brittle.2. The ionic compounds are good conductors of electricity either in fused state or in the form of aqueous solution.3. Ionic Compounds have high melting points and boiling points.4. Ionic compounds have high melting points and boiling points.5. Covalent compounds are mostly volatile.

Covalent Compounds1. Covalent compounds exist in all the three states i.e. gas, liquid and solid.2. A pure covalent compound does not conduct electricity.3. These have usually low melting and boiling points.4. These are soluble in water.5. These are insoluble in water but soluble in organic solvents.

Co-Ordinate Covalent and Covalent Bond

Co-Ordinate Covalent Bond1. It is a bond in which the shared electron pair is denoted by one atom only.2. One atom donates electrons but other has no contribution.3. Lewis acids and bases always from this bond.4. It is represented by ->.5. It is formed by the donation of an electron apir by one of the two bonded atoms.6. It is formed by the completely filled atomic orbital.

Covalent Bond1. It is a bond formed by the mutual sharing of electrons.2. In the shared electron pair both atoms have equal contribution.3. Lewis acids and bases do not form this bond.4. It is represented by _.5. It is formed by the mutual sharing of electrons between atoms.6. It is formed by the overlap of partially filled atomic orbital.

Polar and Non-Polar Covalent Bond

Polar Covalent Bond1. The covalent bond between two atoms having different electro-negativity is called a polar covalent bond.2. In a polar bond, the shared electron pair is not equally attracted by the bonded atoms.3. Bonded atoms become slightly charged and acquire partial =ve and -ve charges.4. It has an ionic character.5. The bond energy is greater.

Non-Polar Covalent Bond1. The covalent bond between two atoms having same electro-negativity is called a non-polar covalent bond.2. In a non polar bond, the shared electron pair is equally attracted by the bonded atoms.3. Bonded atoms remain electrically neutral and do not acquire partial charges.4. It has no ionic character.5. The bond energy is lesser.

Electrolytic and Galvanic or Voltaic Cell

Electrolytic Cell1. It is a device for converting electrical energy into chemical energy. It means by passing current through an electrolyte, chemical reaction takes place.2. It consists of a vessel containing an electrodes and a source of direct current (battery).3. Example: Electrolysis of aqueous solution of NaCl.

Galvanic or Voltaic Cell1. It is a device for converting chemical energy into electrical energy. It means spontaneous redox reaction is used for the production of electric current. This cell was prepared by L.Galvani and A.Volts, hence named as Galvanic or Voltaic Cell.2. It consists of two half-cells. Each half cell consists of an electrodes and the solution with which it is in contact.3. Example: Daniel Cell-Zn/ZnSO4 and Cu/CuSO4 cell.

Solution and Suspension

SolutionThe size of particles is between 0.1 to 1nm.2. Particles cannot be seen with low power microscope.3. It is homogeneous.4. Particles do not settle down.5. It is transparent.6. Components cannot be separated by filtration.

Suspension1. The size of particles is larger than 1000nm.2. Particles can be seen by low power microscope.3. It is heterogeneous.4. Particles settle down.5. It is not transparent.6. Components can be separated by filtration.

The branch of chemistry which deals with the study of chemical energy to electrical energy or electrical energy to chemical energy is called electro-chemistry.

Conductors

Those substances through which electric current can pass are called conductors. For example all metals are conductors.

Non-Conductors

Those substances through which electric current cannot pass are called non-conductors. For example plastic, wood are non-conductors.

Electrolysis

The process in which electricity passes through the aqueous or infused state of some substance. The substances itself decompose into its component. This process is called electrolysis.

Electrolyte

The compound in molten state or in aqueous solution through which electricity can pass are called electrolyte.

Non-Electrolyte

Those compounds through which electricity cannot pass are called non-electrolyte.

Strong Electrolyte

The substances which are highly soluble and completely ionized are called strong electrolyte. For example acids, bases and salts are strong electrolytes.

Weak Electrolyte

The substances which are not highly soluble and remain in un-ionized form are called weak electrolyte.

Electroplating

A process in which metal is deposited on the surface of another metal by electrolysis is called electroplating.

Objectives of Electroplating

DecorationIt is done for decoration. Noble and precious metals like gold or silver are deposited on the inferior metals to enhance their beauty and look beautiful.

ProtectionElectroplating is done to protect the metals from rusting as well as from attack of other substance like organic acids and acidic gases.

RepairIt can be used to repair the broken machinery by electroplating with other metals. Usually the metals like copper, silver, chromium, nickel and gold are used for electroplating.

Procedure of ElectroplatingThe metal which is to be electroplated is first cleaned with sand and then washed with caustic soda solution and finally with a lot of water.This metal is made cathode and the metal which is going to be deposited is made anode. The electrolyte is a salt of metal being deposited and electroplating is carried out in a tank made of cement, glass or wood. It is called an electrolytic tank.The electrolyte should have following properties:1. It must be very soluble in water.2. It must be good conductor.3. Cheap4. May not easily oxidized or reduced or hydrolyzed.(Diagram)

A homogeneous mixture of different chemical substances which has uniform chemical composition through out and shows uniform physical properties is called solution. For example dissolve a small amount of copper sulphate in water the water will become blue. If this blue liquid is filtered, it will pass through the filter paper without leaving any solid. The mixture thus prepared is called a solution.

Binary Solution

A solution which is formed by mixing two substances is called binary solution. For example solution of glucose and water.

Solute

The component of a binary solution which is in lesser amount is called solute. For example in copper sulphate solution, copper sulphate is solute.

Solvent

The component of a binary solution which is in greater amount is called solvent. For example in copper sulphate solution, water is solvent.

Saturated solution

A solution in which maximum amount of a solute has been dissolved at a particular temperature and in which the dissolved form of solute is at equilibrium with its undissolved form is called saturated solution.

Unsaturated Solution

Solution which can dissolve further amount of a solute at a [particular temperature is called an unsaturated solution.

Supersaturated Solution

The solution which contains even more amount of solute required to prepare saturated solution is called super saturated solution. The hot saturated solution of compound like sodium thiosulphate does not crystallize its solute if cooled slowly without disturbance. Such a solution is called supersaturated solution.

Dilute Solution

A solution which contains small amount of a solute as compared to the solvent is called dilute solution.

Concentrated Solution

A solution which contains excess amount of a solute as compared to that of a solvent is called a concentrated solution.

Concentrated Solution

The amount of solute present in given quantity of solvent is called concentration of solution. The concentration of a solution can be expressed in many ways depending upon the amount o solute and solvent present in it.

Concentration of Solution

The amount of solute present in given quantity of solvent is called concentration of solution. The concentration of a solution can be expressed in many ways depending upon the amount of solute and solvent present in it.

Percentage by MassThe percentage of solute by mass is the mass of solute present in hundred part of the solution. For example 5% hydrogen peroxide solution by mass means that 5g hydrogen peroxide are dissolved in 95g of water to give 100g of solution.Percentage of Mass = (Mass of Solute/Mass of Solution) x 100

Percentage by VolumeThe concentration unit expresses the volume of solute present in 100cm3 of solution. For example 15% solution of alcohol by volume will mean that 15cm3 alcohols are present in 100cm3 of solution. (Here 3 represents cube)Percentage by Volume = (Volume of Solute/Volume of Solution) x 100

Molar SolutionThe solution that contains one mole of solute in 1dm3 of solution is called a molar solution. The concentration of this solution is expressed as M.

MolarityMolarity of a solution is the number of moles of solute present in 1dm3 of the solution. It is expressed as M.M = Number of Moles of Solute/Volume of Solution in dm3orM = (Mass of solute/Molecular Mass) x (1/ Volume of Solution in dm3)

Crystallization

The process in which crystal separates from saturated solution on cooling is called crystallization. It is a useful process because it can be used to purify the impure solid compounds. It can also be used to separate a mixture of solids.

Hydration

The ions surrounded by solvent molecules in solution are called solvated ions. If water is a solvent these ions are called hydrated ions.

Suspension

A suspension in such a mixture in which solute particles do not dissolved in solvent and if filtrated its particles do not pass through the pores of filter paper.

Colloidal Solution

In a colloidal solution the solute particles are slightly bigger than those present in a true solution but not big enough to seen with naked eye.

Standard Solution

A solution whose molarity (strength) is known is called Standard Solution.

True Solution

A True Solution is such a mixture in which solute particles are completely homogenized in the solvent for example solution of sodium chloride or copper sulphate in water.

Solubility

Solubility o a solute in a particular solvent is defined as the amount of solute in grams, which can dissolve in 100g of the solvent at a particular temperature to give a saturated solution.orThe amount of a solute in gram moles, which can dissolve in one kilogram of the solvent at a particular temperature, to give a saturated solution.

Factors Affecting the Solubility

Effect of SolventSimilar solvents dissolve similar solutes, i.e. if the chemical structure and the electrical properties such as dipole moment of solute and solvent are similar, the solubility will increase. If there is dissimilarity in properties, then either the solute will not dissolve or there will be very little solubility.

Effect of SoluteDifferent solutes have different solubility’s in a particular solvent e.g. if the saturated solutions of table sugar and sodium chloride are prepared, it is found that the concentration of sodium chloride solution is 5.3 molar while that of sugar solution is 3.8 molar. In other words, the solubility of sodium chloride in water is far greater than that of sugar. This is due to the fact that the attraction of sodium (Na+ and chloride (Cl-) ions with water is greater than that of sugar molecules with water.

Effect of TemperatureChange in temperature has different effects on the solubility of different compounds. Usually the solubility increase with the increase in temperature but it cannot be taken as a general rule. The solubility of compounds like lithium carbonate, calcium chromate decreases with the increase in temperature. The solubility of gases in water also decreases with the increase in temperature. On the other hand, there are a large number of compounds whose solubility in water increase with the increase in temperature e.g. sodium nitrate, silver nitrate, Potassium chloride etc. the solubility of sodium chloride in water does not increase appreciably with the increase in temperature.

Matter has three states:1. Gas2. Liquid3. solidThese are physical states of matter. The three states of one matter may have different physical properties while their chemical properties are same. Water exists in three physical states solid (ice), liquid and gas(steam) has same chemical properties.

Kinetic Theory of Matter

The Kinetic theory was presented to explain the properties of gases and is called kinetic theory of gases. But this theory was also able to explain the composition of liquid and solid state of matter. So its is called Kinetic Theory of Matter.According to Kinetic Theory of matter:1. All matter is composed of atoms, molecules or ions.2. These particles have kinetic energy due to which they are in the state of motion.3. In gaseous state, these particles move in a straight line. They collide with one another and with the walls of container. In liquids the rate of their movement is very small but in solids, there is to and fro motion only.4. Generally material particles can have three types of movements, i.e. translational, rotational and vibrational.

Solids

The state of matter which has definite shape and volume is called solid.

Properties of Solids

1. Definite Volume and ShapeThe cohesive forces in solid substances are so strong that they keep their particles arranged in fixed positions. So due to restrict movements of particles, the solids have definite volume and shape.

2.Motion of ParticlesThe solid particles have vibrational motion only because these particles are held in fixed position by strong cohesive forces.

3. Effect of HeatThe physical state of solid substance can be changed by heating. On heating solid is converted to liquid and gaseous state. Heat increases the kinetic energy of the particles and they start vibrating at higher frequency. At a particular temperature the vibrational motions become fast that they overcome the cohesive forces and solid melts to liquid.

4. Melting PointThe temperature at which the solid is converted to liquid on heating is called melting point. At melting point, the particles of solid loose their means position and their arrangement. The solid collapses and turns to liquid.

5. SublimationThe conversion of some solids directly into gaseous state on heating is called sublimation. Iodine, ammonium chloride and naphthalene change directly into vapour state upon heating.

Liquid

The state of matter having definite volume but indefinite shape is called liquid.

Properties of Liquid

1. VolumeLiquids have definite volume. In liquid particles are very close to one another and have cohesive forces among the particles. Due to the presence of cohesive forces, liquids have definite volume and keep their level as well.

2. ShapeLiquids do not have any specific shape. They adopt the shape of the container. The molecules of liquid are able to move. Due to this random motion the molecules of liquid do not have fixed position and as a result, a liquid does not have any specific shape.

3. EvaporationConversion of liquid into its vapours at any temperature is called evaporation. The molecules of liquid come to the surface of liquid and escape by overcoming cohesive forces. So liquid is converted to vapours at all temperature.

4. Boiling PointThe temperature of a liquid at which its vapour pressure becomes equal to the atmospheric pressure is called boiling point.

Gas

The state of matter which does not have definite shape and volume is called gaseous state.

Properties of Gaseous State

1. Indefinite Volume and ShapeIn gaseous state, the molecules have insignificant cohesive forces among themselves. They move very fast in all possible directions. As a result, a gas neither has fixed shape nor a fixed volume.

2. Kinetic Energy of the Particle of a GasGas particles have very high kinetic energy as compared to liquid and solid state.

3. PressureThe molecules of a gas are in the state of random motion. The molecules of gas not only collide with one another but also with the walls of the container in which they are enclosed. Due to their collision, the velocity of the molecules changes every moment. The pressure exerted by gas is also due to the collision of its molecules with the walls of the container.

4. Elastic CollisionThe collision of gas molecules is elastic in nature which means that the total energy of the colliding molecules remains the same before and after the collision.

5. Kinetic EnergyThe kinetic energy of molecules of gas is very high as compared with solid and liquid.

Diffusion

The movement of molecules from a higher concentration to a lower concentration is known as Diffusion.If the concentration of molecules at a particular place is higher, they start moving towards a place where their concentration is lower. When the concentration of molecules at both the places becomes equal the process of diffusion stops.

Diffusion in Gases

The molecules of one gas can diffuse easily into the molecules of other gas. For example if an open bottle of a perfume is kept in a room, its smell will spread uniformly throughout the room. The liquid perfume present in the bottle volatilized slowly and its vapours diffuse through out the room.

Graham’s Law of Diffusion

Scottish Chemist, Thomas Graham (1833) discovered that lighter gs can diffuse through porous pot faster than the heavier one. This is called Graham’s

Law of Diffusion.Hydrogen being lighter gas will diffuse faster than oxygen or carbon dioxide.

Diffusion in Liquids

Liquid molecules can also diffuse because they have free movement. Since the molecules of liquid move comparatively slowly than gas molecule, their rate of diffusion are also lesser than gases.

Brownian Movement

Robert Brown (1927) discovered this phenomenon:The free movement of the molecules of gases and liquid is called Brownian Movement.”

When a pollen grain is put in water. The movement of pollen grain in water is observed by microscope. It is observed that pollen grain is continuously moving in all directions. This free movement of pollen grain was due to the free movement of water molecules. The colliding water molecules will also force pollen grain to move as well. The students can observe Brownian movement with the help of simple experiment.

Experiment

Put a drop of milk on a microscope slide and cover it with cover slip. Put it under microscope and observe it. You will see small particle of fat moving randomly in milk. The movement of fat particles is actually due to the movement of water molecules in milk.

Periodic Table A table of elements obtained by arranging them in order of their
increasing atomic number in which elements having similar properties are placed
in the same group is called Periodic Table.

Group The vertical column of elements in the periodic table are called Groups.

PeriodThe horizontal rows of elements in the periodic table are called
Periods.

Periodicity The repetition of physical and chemical properties of elements
periodically is called Periodicity of Properties.

Periodic LawPhysical and chemical properties of elements are periodic function of
their atomic masses.

MetalElements which are good conductors of heat and electricity are malleable
and ductile and have a metallic luster are called Metals like Sodium,
Potassium, Gold, Copper etc.

Non-MetalsElements which are non or bad conductor of heat and electricity are
neither malleable or ductile and have no metallic luster are called Non-Metals
like Carbon, Nitrogen, Chlorine etc.

MetalloidsMetalloids are semi metals have the properties which are intermediate
between a metal and non-metal like Boron, Silicon, Germanium, Arsenic, Antimony
etc.

Law of TriadsA German Chemist, Dobereiner (1829), arranged chemically similar
elements in groups of three on the basis of their atomic masses called Triads
and it was found that atomic mass of the middle element was approximately equal
to the average of atomic masses of other two elements. This is known as Law of
Triads.

Drawback or DefectAs very few elements could be arranged in such groups, this
classification did not get wide acceptance.

Law of OctavesAn English Chemist Newland (1864) stated that if the elements were
arranged in the ascending order of their atomic masses, every eight element will
have similar properties to the first. This is knows as Law of Octaves.

Drawback or Defects
1. Noble gases were not discovered at that time and no place was reserved
for the undiscovered noble gases.
2. In the same way no blank spaces for the undiscovered elements were present
in his table.

Mendeleyv’s Period Table and Periodic Law
Russian Chemist, Mendeleyv’s (186) who wa working separately from Lother
Mayer published a table of elements.
According to Mendeleyv’s when the element were arranged in order of their
increasing atomic mases, the elements with similar properties were repeated
after regular interval and were placed one above the other. A table obtained in
this manner is called Periodic Table. Mendeleyv’s stated this periodicity in
the form of Periodic Law.

Important Features of Mendeleyv’s Periodic Table
The important features of Mendeleyv’s Periodic table are:

Periods and Groups
The horizontal rows which run from left to right in Periodic Table are called
Periods and they are twelve in number.
The vertical rows which run from top to bottom in periodic table are called
groups and they are eight in number.

Vacant Spaces
Mendeleyv’s left many vacant spaces for the still unknown elements. For
example, next to Calcium (40) should be Titanium (48) but it resembled silicon
(28) instead of Aluminium (27). He left vacant space for element with atomic
mass 44.

Discovery of New Element
Mendeleyv’s discovered new elements and also guessed their atomic mass and
properties.

Atomic Mass Correction
Mendeleyv’s corrected the atomic masses of certain elements on basis of their
properties and provided proper place to them in the periodic table.

Defects in Mendeleyv’s Periodic Table
The Mendeleyv’s Period Table has following defects:

Irregular Position of Some Elements
According to Mendeleyv’s Periodic Law Potassium (39) should be placed before
Argon (40) but he placed Argon (40) before Potassium (39) which goes against
his law.

Position of Isotopes
Mendeleyv’s periodic table gives no indication about the position of isotopes.

Structure of Atom
Mendeleyv’s Periodic table gives no idea about structure of atoms.

Position of Lanthanides and Actinides
Lanthanides and Actinides have not been given proper place in Periodic Table.

Coinage and Alkali Metals
Alkali metals and coinage metals with different properties are placed in the
same group. This defect has been replaced by placing them into two sub groups.

Modern Periodic Law and Modern Periodic Table

Modern Periodic Law
Physical and chemical properties of the elements are periodic function of their
atomic number. Mosely (1913) says that atomic mas is not fundamental property.
Due to some defects present in Mendeleyv’s periodic law, Mosely introduced the
concept of anomic number for the elements.

Example
When isotopes were discovered, it was thought advisable to arrange the elements
on basis of their atomic number instead o increasing atomic mases. Isotopes
were needed different position in the Mendeleyv’s periodic table. Hence
Mendeleyv’s periodic law was modified.

Modern Periodic Table
When Mendeleyv’s periodic law was modified and new elements were discovered.
This forcd the scientists to change Mendeleyv’s periodic law.
The electronic configuration of atoms also played an important role in he
arrangement of the modern periodic law. This form of periodic table is called
“Long form of Periodic Table” because it contains eighteen groups instead of
eight but seven periods instead of twelve.

Group I – The Alkali Metals
The elements of group I are called “Alkali Metals”. The word alkali is
derived from an Arabic word meaning Ashes.

Elements of Group I
Lithium
Sodium
Potassium
Rubidium
Cesium
Francium

Properties of Group I
1. They are mono atomic.
2. They exist in solid metallic state.
3. Outer most shell of these elements is incomplete having one electron.
4. Elements of this group are highly reactive.
5. Elements of this group have large tendency to form compounds.
6. Elements of this group are strongly electro-positive.

Group II – The Alkaline Earth Metals
The elements of group II are called Alkaline Earth Metals. These elements
occur in nature as silicate mineral and their oxides and hydroxides are
strongly basic. Therefore these elements are called Alkaline Earth Metals.

Properties of Group II
1. They are mono atomic.
2. They exist in solid state.
3. Outer most shell of these elements is incomplete having two electrons.
4. Elements of this group are moderately reactive.
5. Elements of this group have moderate tendency to form compounds.

Group III – The Boron or Aluminium Family
The elements of group III exist in solid state.

Properties of Group III
1. They are mono atomic.
2. They exist in solid state.
3. Outer most shell of these elements is incomplete having three electrons.
4. Elements of this group are quite reactive.
5. Elements of this group have moderate tendency to form compounds.

Group IV – The Carbon and Silicon Family

Elements of Group IV
Carbon
Silicon
Germanium
Tin
Lead

Properties of Group IV
1. They are mono atomic.
2. They exist in solid state.
3. Outermost shell of these elements is incomplete.
4. Elements of this group are quite reactive.
5. Elements of this group have moderate tendency to form compounds.

Group V – The Nitrogen Family

Elements of Group V
Nitrogen
Phosphorus
Arsenic
Antimony
Bismuth

Properties of Group V
1. Some are mono atomic and some are di-atomic.
2. Some of them exist in gaseous and some are in solid state.
3. Outermost shell of these elements is incomplete having five electrons.
4. elements of this group are quite reactive.
5. Elements of this group have quite tendency to form compound.

Group VI – The Oxygen Family

Elements of Group VI
Oxygen
Sulphur
Selenium
Tellurium
Polonium

Properties of Group VI
1. Some are mono atomic and some are di-atomic.
2. Some of them exist in gaseous and some are in solid state.
3. Elements of this group have quite tendency to form compounds.
4. The tendency of forming covalent bond decreases from oxygen to polonium.
5. There is a gradual decrease in the ionization potential down the group.

Properties of Group VII
1. They are diatomic except At.
2. Halogens are very active non-metals.
3. Outer most shell of these elements is incomplete having seven electrons.
4. Elements of this group are highly reactive.
5. There is a gradual decrease in the ionization potential down the group.

Transition ElementsDefinition
Elements in Group IB, IIB, through VIIB are known as Transition Elements
because they show their properties which are transitional between higly
reactive and strong electro-positive elements of S-block which form ionic
compounds and p-block elements which form largely covalent compounds.

Properties of Transition Elements
1. Transition Elements have incomplete inner electron shells.
2. They show variable valency.
3. They show similar behaviour.
4. They all are metals.
5. They have strong inner atomic bonds.

Group 0, The Noble GasesThe elements of Group VIII A are called “Noble Gases” or “Inert Gases”
or “Zero Group Elements”.

Elements of Group 0
Helium
Neon
Argon
Krypton
Xenon
Radon

Properties of Group 0
1. They are mono atomic.
2. They exist in gaseous state.
3. Outer most shell of these elements is either complete or contains eight
electrons.
4. These elements are mostly chemically non-reactive.
5. These elements have no tendency to form compounds (only a few of these
compounds are known).

Atomic Radius DefinitionOne half of the distance between the nucleus of two identical atoms when
these are in close contact with each other is called Atomic Radius.

Unit
It is measured in angstrom unit A.

Trend in Period
The atomic radii decreases from left to right within a period in the periodic
table. This is because nuclear charge increases with the increase of atomic
number. But the number of shells remains same within a period.

Trend in Group
Atomic radius increases from top to bottom in a group. This is because,
although nuclear charge increases from top to bottom but at the same time on
new shell is also added for each successive element down the group.

Ionization Energy (I.E) or Ionization Potential (I.P)Definition
The minimum energy needed to remove an electron from an isolated, gaseous atom
in its ground state is called Ionization Energy.

Factors Affecting Ionization Energy
The ionization energy of elements depends upon the following factors:
1. Effect of Nuclear Charge on I.E
The greater the nuclear charge the higher is the ionization energy.
2. Effect of Atomic Size
The larger the size of atom the lower is the ionization energy.

Trend of I.E in Period
Ionization energy increases from left to right in a period due to increase in
nuclear change and decrease in atomic size.

Trend of I.E in Group
I.E decreases from top to bottom in a group due to increase in atomic size.

ElectronegativityDefinition
The tendency of each atom in a covalent molecule to attract a shared pair of
electrons towards itself is known as its electronegativity.

Trend or Variation in the Period
Electronegativity increases from left to right within a period due to increase
in nuclear charge and decrease in atomic size.

Trend or Variation in the Group
Electronegativity values decreases from top to bottom within a group due to
increase in atomic size.

Electron AffinityDefinition
The energy change that occurs when an electron is gained by an atom in the
gaseous state is known as Electron Affinity.
Electron Affinity for the addition of first electron is negative i.e. energy is
released but for further addition of electrons it is positive because energy
has to be added to over come repulsion between negative ion and electron.

Unit
It is measured in KJ/mol or in e.v per atom.

Factors Affecting Electron Affinity
Atomic Size
Nuclear Charge

Trend or Variation of Electron Affinity in Group
Down the group in the periodic table, electron affinity decreases because the
addition of a new shell to each atom decreases its force of attraction.

Trend or Variation of Electron Affinity in Period
In a period, the electron affinity increases from left to right because the
incoming successive atoms have higher nuclear charge and attract electron more
towards itself.

The important postulates of Dalton’s atomic theory are:
1. All elements are composed of atoms. Atom is too small so that it could not be divided into further simpler components.
2. Atom cannot be created nor destroyed in any chemical reactions.
3. Atoms of an element are similar in all respects. They have same mass and properties.
4. Atoms of different elements combine in a definite simple ratio to produce compounds.Discovery of Electron

A discharge tube is a glass tube. It has two electrode, a source of electric current and a vacuum pump.
(Diagram)
Sir William Crooks (1895 performed experiments by passing electric current through gas in the discharge tube at very low pressure. He observed that at 10-4 (-4 is power to 10) atmosphere pressure, shining rays are emitted from cathode. These rays were named cathode rays. Cathode rays are material particles as they have mass and momentum.

Properties of Cathode Rays

The properties of these particles are given below:

1. These particles are emitted from cathode surface and move in straight line.
2. The temperature of the object rises on which they fall.
3. They produce shadow of opaque object placed in their path.
4. These particles are deflected in electric and magnetic fields.
5. These particles are deflected towards positive plate of electric field.

Discovery of Proton

Gold Stein (1886) observed that in addition to the cathode rays, another type of rays were present in the discharge tube. These rays travel in a direction opposite to cathode rays. These rays were named positive rays. By using perforated cathode in the discharge tube the properties of these rays can be studied. Positive rays are also composed of metered particles. The positive rays are not emitted from anode. They are produced by the ionization of residual gas molecules in the discharge tube. When cathode rays strike with gas molecule, electrons are removed and positive particles are produced.

2. The mass of positive rays is equal to the mass of the gas enclosed in the discharge tube.
3. The minimum mass of positive particles is equal to the mass of hydrogen ion (H+). These positive ions are called Protons.
4. The charge on proton is equal to +1.602×10-19 Coulomb. (-19 is power of 10)

Natural Radioactivity

The phenomenon in which certain elements emit radiation which can cause fogging of photographic plate is called natural radioactivity. The elements which omit these rays are called radioactive elements like Uranium, Thorium, Radium etc. There are about 40 radioactive elements. Henri Bequrel (1896) discovered radioactivity.Madam Curei also has valuable contribution in this field.
In natural radioactivity nuclei of elements are broken and element converted to other elements. Natural radioactivity is nuclear property of the elements.

Alpha Rays

1. They are helium nuclei. They are doubly positively charged, He2+.

2. They move with speed equal to the 1/10th of the velocity of the light.
3. They cannot pass through thick-metal foil.
4. They are very good ionizer of a gas.
5. They affect the photographic plate.

Beta Rays

1. They are negatively charged.
2. They move with the speed equal to the velocity of light.
3. They can pass through a few millimeter thick metal sheets.
4. They are good ionizer of a gas.
5. They can affect the photographic plate.

Gamma Rays

1. They are electromagnetic radiations.
2. They travel with speed equal to velocity of light.
3. They carry no charge.
4. They have high penetration power than alpha and beta rays.
5. They are weak ionizer of gas.

Rutherford Experiment and Discovery of Nucleus

Lord Rutherford (1911) and his coworkers performed an experiment. They bombarded a very thin, gold fail with Alpha particles from a radioactive source. They observed that most of the particles passed straight through the foil undeflected. But a few particles were deflected at different angles. One out of 4000 Alpha particles was deflected at an angle greater than 150.
(Diagram)

Conclusion

Following conclusions were drawn from the Rutherford’s Alpha Particles scattering experiment.
1. The fact that majority of the particles went through the foil undeflected shows that most of the space occupied by an atom is empty.
2. The deflection of a few particles over a wide angle of 150 degrees shows that these particles strike with heavy body having positive charge.
3. The heavy positively charged central part of the atom is called nucleus.
4. Nearly all of the mass of atom is concentrated in the nucleus.
5. The size of the nucleus is very small as compared with the size of atom.

Defects of Rutherford Model

Rutherford model of an atom resembles our solar system. It has following defects:
1. According to classical electromagnetic theory, electron being charged body will emit energy continuously. Thus the orbit of the revolving electron becomes smaller and smaller until it would fall into the nucleus and atomic structure would collapse.
2. If revolving electron emits energy continuously then there should be a continuous spectrum but a line spectrum is obtained.
(Diagram)

Bohr’s Atomic Model

Neil Bohr (1913) presented a model of atom which has removed the defects of Rutherford Model. This model was developed for hydrogen atom which has only proton in the nucleus and one electron is revolving around it.

Postulates of Bohr’s Atomic Model

The main postulates of Bohr’s Model are given below:
1. Electrons revolve around the nucleus in a fixed orbit.
2. As long as electron revolves in a fixed orbit it does not emit and absorb energy. Hence energy of electron remains constant.
3. The orbit nearest to the nucleus is the first orbit and has lowest energy. When an electron absorbs energy it jumps from lower energy orbit to higher energy orbit. Energy is emitted in the form of radiations, when an electron jumps from higher energy orbit to lower energy orbit. The unit of energy emitted in the form of radiations is called quantum. It explains the formation of atomic spectrum.
4. The change in energy is related with the quantum of radiation by the equation :
E2 – E1 = hv
where
E1 = Energy of first orbit
E2 = Energy of the second orbit
h = Planck’s constant
v = Frequency of radiation

Atomic Number

The number of protons present in the nucleus of an atom is called atomic number or proton number. It is denoted by z. The proton in the nucleus of an atom is equal to number of electrons revolving around its nucleus.

Mass Number

The total number of the protons and neutrons present in the nucleus of an atom is called mass number. The protons and neutrons together are called nucleon. Hence it is also known as nucleon number. It is denoted by A. the number of neutrons present in the nucleus of an atom is rperesented by N.
Mass Number = No of Protons + No of neutrons
A = Z + N

Isotopes

The atoms of same elements which have same atomic number but different mas number are called Isotopes. The number of protons present in the nucleus of an atom remains the same but number of neutrons may differ.Isotopes of Different Elements

Protium
Ordinary naturally occurring hydrogen contains the largest percentage of protium. It is denoted by symbol H. It has one proton in its nucleus and one electron revolve around the nucleus.
Number of Protons = 1
Number of Electrons = 1
Number of Neutrons = 0
Atomic Number = 1
Mass Number = 1

Deutrium
Deutrium is called heavy hydrogen. The percentage of deutrium in naturally occuring hydrogen is about 0.0015%. It has one proton and one neutron in its nucleus. It has one electron revolving around its nucleus. It is denoted by symbol D.
Number of Proton = 1
Number of Electron = 1
Number of Neutrons = 1
Atomic Number = 1
Mass Number = 2

Tritium
Radioactive hydrogen is called tritium. It is denoted by symbol T. The number of tritium isotope is one in ten millions. It has one proton and 2 neutrons in its nucleus. It has one electron revolving around its nucleus.
Number of Proton = 1
Number of Electron = 1
Number of Neutron = 2
Atomic Number = 1
Mass Number = 3